<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
       body {
    font-family: "Lato", sans-serif;
}

.sidenav {
    display: none;
    height: 100%;
    width: 250px;
    position: fixed;
    z-index: 1;
    top: 0;
    left: 0;
    background-color: #111;
    overflow-x: hidden;
    padding-top: 60px;
}

.sidenav a {
    padding: 8px 8px 8px 32px;
    text-decoration: none;
    font-size: 25px;
    color: #818181;
    display: block;
}

.sidenav a:hover, .offcanvas a:focus{
    color: #f1f1f1;
}

.sidenav .closebtn {
    position: absolute;
    top: 0;
    right: 25px;
    font-size: 36px;
    margin-left: 50px;
}

@media screen and (max-height: 450px) {
  .sidenav {padding-top: 15px;}
  .sidenav a {font-size: 18px;}
}
    </style>
</head>
<body>
    <div id="mySidenav" class="sidenav">
        <a href="javascript:void(0)" class="closebtn" onclick="closeNav()">&times;</a>
        <a href="#">About</a>
        <a href="#">Services</a>
        <a href="#">Clients</a>
        <a href="#">Contact</a>
      </div>
      
      <h2>侧边栏</h2>
      <p>点击以下菜单图标打开侧边栏。</p>
      <span style="font-size:30px;cursor:pointer" onclick="openNav()">&#9776; 打开</span>
</body>
</html>
<script>
 function openNav() {
    document.getElementById("mySidenav").style.display = "block";
}

function closeNav() {
    document.getElementById("mySidenav").style.display = "none";
}
</script>